The move was not motivated by a specific terror plot, said Kip Hawley, the assistant secretary at the Department of Homeland Security in charge of aviation security. But there is concern both in the United States and internationally that common remote-control toys could be used to detonate a bomb as part of a terror plot.

The aviation authorities decided against banning the devices in carry-on bags. But people carrying remote-control toys — including children — could be subject to a more intense search, in which the passenger is patted down and the baggage is checked by hand, officials said.

The new policy comes just days after the federal authorities in South Carolina disclosed that a Florida college student arrested in August on explosive-related charges had made a video that he posted on YouTube showing how to use such a remote-control toy as a detonator.

Hawley acknowledged in an interview Monday that this video played a role in the new policy. But it was just one piece of intelligence that led to the change. Remote-control toys might have been used already by terrorists in Sri Lanka and India, one federal official noted.

“A lot of that work is sorting through dots,” Hawley said of the different intelligence leads that produced the heightened scrutiny. “This is a dot that just came up with enough granularity that it seemed we should take direct action on it.”

The federal authorities considered simply making the change at airports in the United States without announcing it. But instead they decided to disclose the new policy, while encouraging passengers to put remote-control toys in checked luggage to avoid the additional scrutiny at the checkpoint, Hawley said.

“Everybody knows there is an intelligence and law enforcement community out there, that there are people seeking to do us harm,” he said. “This is just the tangible manifestation of that.”

The new scrutiny for remote-control toys will not extend to devices that automatically open car doors or to television remote controls, a TSA spokeswoman said.

In the South Carolina case, the authorities found a 12-minute Arabic language video on the computer of Ahmed Abdellatif Sherif Mohamed, an Egyptian student at University of South Florida. A narrator in the video explains how to convert a toy car into a detonator for a bomb, a search warrant affidavit filed in federal court in Charleston, S.C., on Thursday says.

Mohamed had been arrested in August after he was found near a South Carolina military base driving a car that had what the authorities described as bomb-making parts in the trunk, including plastic pipes, potassium nitrate and a safety fuse cord. Immediately after the arrest, which started as a speeding case, friends and family of Mohamed said the charges were unwarranted, asserting that the materials in the car would be, if assembled, not much more powerful than firecrackers.